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141.
Enantiomeric separation of new phytoalexin analogs with cyclofructan chiral stationary phases in normal‐phase mode
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Marianna Moskaľová Ján Petrovaj Taťána Gondová Mariana Budovská Daniel W. Armstrong 《Journal of separation science》2016,39(19):3669-3676
For the first time, three different derivatized cyclofructan chiral stationary phases were used for the direct high‐performance liquid chromatographic enantiomeric separation of 11 new racemic analogs of a natural indole phytoalexin. This class of compounds is known to have significant antiproliferative activity and other potentially useful pharmacological properties. The effect of various experimental factors was investigated to optimize the separations in the normal‐phase mode. It was found that the nature of polar modifier and additive in the mobile phase have significant impact on the enantioseparations. Better chiral recognition of analyzed compounds was achieved on (R)‐naphthylethyl carbamate cyclofructan 6 than on isopropyl carbamate cyclofructan 6 and dimethylphenyl carbamate cyclofructan 7. The thermodynamic parameters showed that the chiral separation was enthalpy controlled in all cases. 相似文献
142.
Merlino A Boiani M Cerecetto H González M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(2):540-549
The spectroscopic behavior of 2-benzyl-2-methyl-2H-benzimidazole 1,3-dioxide derivatives in solution was studied in terms of electronic and nuclear magnetic resonance ((1)H and (13)C NMR) techniques. The experimental spectra were compared to the theoretical ones, obtained at DFT level, proving that the compounds adopt in solution a bird-like conformational distribution. Also, theoretically this conformational distribution resulted the most stable in gas phase. Infrared spectroscopy was used to study solid state behavior identifying experimentally the N-O stretching near to 1380, 1365 and 1225 cm(-1) and the vibrational benzimidazole skeleton near to 1610 and 1590 cm(-1). The vibrational spectrum was satisfactorily described by DFT calculations funding the N-O stretching as a coupled vibration near to 1470, 1350 and 1285 cm(-1). The fragmentation that takes place in mass spectrometry was assigned for all of the new derivatives. 相似文献
143.
Boneva MP Christov NC Danov KD Kralchevsky PA 《Physical chemistry chemical physics : PCCP》2007,9(48):6371-6384
Here, we investigate experimentally and theoretically the motion of spherical glass particles of radii 240-310 microm attached to a tetradecane-water interface. Pairs of particles, which are moving toward each other under the action of lateral capillary force, are observed by optical microscopy. The purpose is to check whether the particle electric charges influence the particle motion, and whether an electric-field-induced capillary attraction could be detected. The particles have been hydrophobized by using two different procedures, which allow one to prepare charged and uncharged particles. To quantify the hydrodynamic viscous effects, we developed a semiempirical quantitative approach, whose validity was verified by control experiments with uncharged particles. An appropriate trajectory function was defined, which should increase linearly with time if the particle motion is driven solely by the gravity-induced capillary force. The analysis of the experimental results evidences for the existence of an additional attraction between two like-charged particles at the oil-water interface. This attraction exceeds the direct electrostatic repulsion between the two particles and leads to a noticeable acceleration of their motion. 相似文献
144.
Silva OF Silber JJ de Rossi RH Correa NM Fernandez MA 《The journal of physical chemistry. B》2007,111(36):10703-10712
The formation of reverse micelles (RMs) of sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT) in n-heptane including two different beta-cyclodextrin (beta-CD) derivatives (hydroxypropyl-beta-CD, hp-beta-CD, and decenyl succinyl-beta-CD, Mod-beta-CD) is reported. Both cyclodextrins can be incorporated into AOT RMs in different zones within the aggregate, while beta-CD cannot. Using UV-vis and induced circular dichroism (ICD) spectroscopy and different achiral molecular probes (some azo dyes, p-nitroaniline and ferrocene), it was possible to determine that Mod-beta-CD is located with its cavity at the oil side of the AOT RM interface, while for hp-beta-CD the cavity is inside the RM water pool. Among the molecular probes used, methyl orange (MO) was the only one which gave the ICD signal when dissolved in the AOT RMs with hp-beta-CD, so a detailed study of MO behavior in homogeneous media was also performed to compare with the microheterogeneous media. The solvatochromic behavior of the dye depends not only on the polarity of the media but also on other specific solvent properties. A Kamlet-Taft analysis shows that the MO absorption spectrum shifts to longer wavelength with an increase in the solvent polarity-polarizability (pi*) and the hydrogen donor ability (alpha) of the medium. MO appears to be almost 3 times more sensitive to the pi* parameter than to the alpha parameter. In addition, from the MO absorption spectral changes with the hp-beta-CD concentration, the association equilibrium constants in pure water (K11W) and inside the RMs (K11RM) were computed. The results show that K11W is almost 10 times larger than the value inside the RMs. The latter can be explained considering that MO resides anchored to the RM interface through hydrogen bond interaction with the hydration bound water. This study shows for the first time that the cyclodextrin chiral cavity is available for a guest in an organic medium such as the RMs; therefore, we have created a potentially powerful nanoreactor with two different confined regions in the same aggregate: the polar core of the RMs and the chiral hydrophobic cavity of cyclodextrin. 相似文献
145.
Agibert SA Moreira MB Ratusznei SM Rodrigues JA Zaiat M Foresti E 《Applied biochemistry and biotechnology》2007,136(2):193-206
The effect of temperature on the performance of an anaerobic sequencing biofilm batch reactor (ASBBR) with liquid-phase recirculation
was assessed. Assays were performed using a recirculation velocity of 0.20 cm/s, 8-h cycles, and an average treated synthetic
wastewater volume of 2 L/cycle with a concentration of 500 mg of Chemical Oxygen Demand (COD)/L. Operation temperatures were
15, 20, 25, 30, and 35°C. At 25, 30, and 35°C, organic matter removal efficiencies for filtered samples ranged from 81 to
83%. At lower temperatures, namely 15 and 20°C, removal efficiency decreased significantly to 61 and 65%, respectively. A
first-order model could be fitted to the experimental concentration profile values. The first-order kinetic parameter value
of this model varied from 0.46 to 0.81 h1 considering the lowest and highest temperature studied. Moreover, analysis of the removal profile values allowed fitting
of an Arrhenius-type equation with an activation energy of 5715 cal/mol. 相似文献
146.
Milen G. Bogdanov Mariana D. Palamareva Blagovesta T. Gocheva Darina B. Dimitrova 《Journal of heterocyclic chemistry》2007,44(3):673-677
147.
Mariana Sardo Ana M. Amado Paulo J. A. Ribeiro‐Claro 《Journal of Raman spectroscopy : JRS》2009,40(12):1956-1965
The importance of hydrogen‐bond formation in the molecular packing arrangements of two anhydrous forms of nitrofurantoin is investigated, combining computational methods and spectroscopic data. The overall results indicate, as expected, that the vibrational modes related to the CO, N H and C H groups are strongly affected by intermolecular hydrogen‐bond formation. Moreover, the importance of weak C‐H···O interactions in conferring additional stability to molecular associations in biological systems is evidenced in this study. The complete assignment of the Raman and infrared spectra of both polymorphs is accomplished by means of a computationally based methodology, which accounts for the effects of intermolecular interactions in the crystal. The vibrational shifts due to crystal packing interactions are evaluated from DFT calculations for a set of suitable molecular pairs, using the B3LYP/6‐31G* approach. This methodology provides an answer to the current demand for a reliable and complete assignment of the vibrational spectra of pharmaceutically active compounds such as nitrofurantoin. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
148.
Marjorie C. L. C. Freire Gabriela D. Noske Natlia V. Bitencourt Paulo R. S. Sanches Norival A. Santos-Filho Victor O. Gawriljuk Eduardo P. de Souza Victor H. R. Nogueira Mariana O. de Godoy Aline M. Nakamura Rafaela S. Fernandes Andre S. Godoy Maria A. Juliano Bianca M. Peres Cecília G. Barbosa Carolina B. Moraes Lucio H. G. Freitas-Junior Eduardo M. Cilli Rafael V. C. Guido Glaucius Oliva 《Molecules (Basel, Switzerland)》2021,26(16)
The COVID-19 outbreak has rapidly spread on a global scale, affecting the economy and public health systems throughout the world. In recent years, peptide-based therapeutics have been widely studied and developed to treat infectious diseases, including viral infections. Herein, the antiviral effects of the lysine linked dimer des-Cys11, Lys12,Lys13-(pBthTX-I)2K ((pBthTX-I)2K)) and derivatives against SARS-CoV-2 are reported. The lead peptide (pBthTX-I)2K and derivatives showed attractive inhibitory activities against SARS-CoV-2 (EC50 = 28–65 µM) and mostly low cytotoxic effect (CC50 > 100 µM). To shed light on the mechanism of action underlying the peptides’ antiviral activity, the Main Protease (Mpro) and Papain-Like protease (PLpro) inhibitory activities of the peptides were assessed. The synthetic peptides showed PLpro inhibition potencies (IC50s = 1.0–3.5 µM) and binding affinities (Kd = 0.9–7 µM) at the low micromolar range but poor inhibitory activity against Mpro (IC50 > 10 µM). The modeled binding mode of a representative peptide of the series indicated that the compound blocked the entry of the PLpro substrate toward the protease catalytic cleft. Our findings indicated that non-toxic dimeric peptides derived from the Bothropstoxin-I have attractive cellular and enzymatic inhibitory activities, thereby suggesting that they are promising prototypes for the discovery and development of new drugs against SARS-CoV-2 infection. 相似文献
149.
In this work we perform an ab initio study of the electric field gradient (EFG) at the nucleus of Fe impurities in crystalline SnO. The Augmented Plane Waves plus Local Orbitals method is used to obtain the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the SnO host in a fully self-consistent way. Most calculations are performed assuming that Fe ions replace the Sn atoms of the structure, in some cases including oxygen vacancies in order to discuss their role in the hyperfine interactions and in determining the local structure around Fe impurities. The case of interstitial Fe sites is also considered. Our predictions are compared with available Müssbauer spectroscopy results and also with theoretical and experimental results obtained for rutile SnO2 and TiO2. 相似文献
150.
Fifere Adrian Tania Budtova Elena Tarabukina Mariana Pinteala Spulber Mariana Cristian Peptu Valeria Harabagiu Bogdan C. Simionescu 《Journal of inclusion phenomena and macrocyclic chemistry》2009,64(1-2):83-94
Carboxyl modified γ-cyclodextrin (CDSA) with a substitution degree of about 9.5 was prepared by the esterification of γ-cyclodextrin (CD) with succinic anhydride in pyridine at 90 °C. The chemical composition and the structure of CDSA were characterized by FT-IR, MALDI-TOF, X-ray diffraction pattern, potentiometric titration and TGA. Modified and native γ-cyclodextrin associate with fullerene (C60) in DMF-toluene mixture resulting 1:1 CDSA:C60 and CD:C60 inclusion complexes. Aqueous solutions of native cyclodextrin, carboxyl-modified cyclodextrin and their inclusion complexes with C60 were used as microgel solvent (or swelling agent) for controlled release application. The release of solutions was induced by shear stress and demonstrated using rheo-optical set-up. 相似文献